The present invention relates to the field of fiber-optics.
Previous nonlinear fiber devices relied on phase-matched, third order effects (cf. R. Stolen and J. Bjorkhjolm, IEEE J.Q.E. QE-18, 1062 (1982) or were not phase-matched at all (cf. C. Koster, IEEE J.Q.E. QE-2, 580 (1966) and E. S. Goldburt and P. Russell, Appl. Phys. Lett. 46,338 (1985) and T. Bridges, A. Chraplyvy, J. Bergman and R. Hart, Opt. Lett. 6, 632 (1981). No phase-matched, second order processes like frequency doubling or three-wave parametric mixing have been publicized. Although planar waveguides have been used previously for second harmonic generation (cf. G. Hewig and K. Jain, J. Appl. Phys. 59, 57 (1983)), these devices have mode structures and refractive indices poorly matched to fiber optic systems, as well as low efficiencies.
It is an object of the present invention to produce a device which facilitates efficient, second-order nonlinear optical mixing of low power, coherent light sources and frequency doubling encoding, in fiber-optic systems, and to provide efficient modulators, and parametric amplifiers which are second-order in the optical fields. Prior art devices have produced only linear optical devices in which properties dependent on a single field amplitude or third (or higher) order field amplitudes. The device of the present invention provides phase-matched output dependent on only two field amplitudes.
One important application of the present invention is to double the frequency of IR laser light, having a wavelength of, for example, 1.3-1.5 microns, transmitted through a fiber before it illuminates a detector which functions more efficiently at the doubled frequency. Another application is to encode data by frequency doubling to thwart unauthorized tapping of the data.